The present application is related to and claims priority from Japanese Patent Application No. 11-329212, filed Nov. 19, 1999.
The present invention relates to a liquid crystal display device, and more particularly, to an insulative substrate on which to form interconnecting patterns for a liquid crystal display element using thin film transistors or the like as its switching elements as well as to a liquid crystal display element using such an insulative substrate.
In a semiconductor device such as an active matrix type of liquid crystal display element which uses thin film transistors (TFTs) as switching elements for its pixels, current paths such as interconnecting patterns or electrodes are formed over an insulative substrate out of conductive thin films.
In a liquid crystal display element in particular, with recent increases in its display area and in the scale of its integration, a reduction in the resistance of its internal interconnection lines has become an important subject. In a TFT type of liquid crystal display element, scanning signals and video signals are supplied from an end side of an interconnecting pattern, so that as the distance from a power feeding point becomes larger, distortions occur in signal waveforms due to the resistance values of interconnection lines, causing a display defect.
For this reason, investigation has been made into how a low-resistance material which can be substituted for chromium (Cr) which has heretofore been generally used is to be adopted as a material for forming interconnection lines or electrodes (hereinafter referred to as interconnection lines or the like). In addition, molybdenum (Mo) is known as one of promising candidates for materials which form metal films such as interconnection lines, from all possible points of view such as the degree of reduction in resistance value, adaptability to an etching process for patterning the interconnection lines and the like, the complexity of a manufacturing process, film stress and environment protection.
In general, the formation of this kind of interconnection line or the like is carried out by subjecting a conductive thin film formed over an insulative substrate (typically, a glass substrate in a liquid crystal display element) to mask exposure using a photosensitive resist, development and patterning using etching treatment, i.e., by using a photolithographic technique.
However, a film of Mo is disadvantageous in that the adhesion of the Mo film to a base substrate (such as a glass substrate in a liquid crystal display element or a silicon substrate in a semiconductor device such as a large-scale integrated circuit) is insufficient so that the Mo film easily peels from the base substrate, and in that if a resist is applied to the Mo film, the resist does not sufficiently adhere, and no desired etching accuracy is obtained. For this reason, it has heretofore been general that if Mo is to be used, another element is added to Mo to form a Mo alloy.
However, the formation of the alloy increases the resistance values of interconnection lines or the like, and causes an increase in the cost of a material such as a sputtering target which is used in a manufacturing process.
The defective adhesion of the metal film to the base substrate originates in the properties of the insulative substrate and the Mo film themselves as well as in the contamination of the surfaces of the insulative substrate and the Mo film. In general and in terms of surface contamination, treatments such as cleaning with various kinds of fluids and in-vacuum heating are performed before or after the formation of thin films such as interconnection lines.
In addition, for example, Japanese Patent Laid-Open No. 162161/1997 has a description to the effect that etching accuracy can be improved by performing surface reforming on a metal film by oxygen plasma ashing before the metal film is etched after the formation of a resist pattern. In terms of the properties of the film itself, although there is a method which uses an alloy of a high-melting point metal such as Mo, chromium (Cr) or tungsten (W), the structure described in U.S. Pat. No. 4,429,011 uses a method of nitriding the surface of a film of Mo and forming a nitride for surface stabilization. In addition, for example, Japanese Patent Laid-Open No. 161140/1998 describes a method of forming a nitride film on an interconnection film of a high-melting point metal for the purpose of reducing the pressure-contact resistance of connecting electrodes.
Although the prior-art pretreatment such as the cleaning of an insulative substrate and in-vacuum heating is generally performed by those skilled in the art, it cannot be said that the prior art can sufficiently remove contamination. The method described in Japanese Patent Laid-Open No. 162161/1997 performs oxygen plasma treatment after the formation of a resist pattern, but it is not clear whether this method contributes to the adhesion of a resist to an insulative substrate (substrate adhesion, i.e., base adhesion) and the adhesion of the resist.
In the method of forming a nitride layer (nitride film) on the surface of an insulative substrate as described in U.S. Pat. No. 4,429,011, after a Mo interconnecting pattern has been formed, the formed pattern is treated in ammonium atmosphere at 400-850xc2x0 C., but it is not clear how a thin film forming element is influenced by the exposure of the insulative substrate to high temperatures.
In addition, the above-described prior art adopts a method which, after forming thin films such as interconnection lines on an insulative substrate, temporarily takes the insulative substrate out of a vacuum chamber, and performs treatment on the insulative substrate in a separate apparatus after exposing the insulative substrate to atmospheric air for a predetermined time. This method causes problems such as the risk of adsorption of atmospheric impurities to the surface of the insulative substrate, a reduction in production efficiency due to the use of the separate apparatus, and an increase in the cost of a manufacturing apparatus.
Moreover, in the method described in Japanese Patent Laid-Open No. 161140/1998, although it is asserted that the pressure-contact resistance can be restrained by the formation of the nitride film, it is not clear whether the substrate adhesion and the resist adhesion can be improved.
In one embodiment of the present invention, a liquid crystal display includes an insulative substrate having a surface treated with an oxygen plasma and a nitrogen-plasma-treated layer formed over said surface of said substrate. A surface of said nitrogen-plasma-treated layer has a nitrogen concentration of about 10 mol % or more.
In another embodiment, a liquid crystal display includes at least one glass substrate having a surface treated with an oxygen plasma. A protective layer is formed over the surface by igniting a nitrogen plasma over the surface. A conductive layer is formed over the protective layer, where the conductive layer includes a metallic element. A lower conductive layer is provided below the conductive layer, where the lower conductive layer has the metallic element and nitrogen atoms. An upper conductive layer is provided above the conductive layer, where the upper conductive layer has the metallic element and nitrogen atoms. The protective layer has a nitrogen concentration of about 10 mol % or more.
The present invention is not limited to any of the above-described constructions and embodiments which will be described below, and various modifications of the present invention can be made without departing from the technical ideas described in the appended claims.